Michigan Technological University Digital Commons @ Michigan Tech Dissertations, Master's Theses and Master's Reports 2016 Rhyolite and Trachyte Formation at Lake City Caldera: Insight from Quantitative Textural and Geochemical Analyses Jordan Lubbers Michigan Technological University, [email protected] Copyright 2016 Jordan Lubbers Recommended Citation Lubbers, Jordan, "Rhyolite and Trachyte Formation at Lake City Caldera: Insight from Quantitative Textural and Geochemical Analyses", Open Access Master's Thesis, Michigan Technological University, 2016. https://doi.org/10.37099/mtu.dc.etdr/99 Follow this and additional works at: https://digitalcommons.mtu.edu/etdr Part of the Geochemistry Commons, and the Geology Commons RHYOLITE AND TRACHYTE FORMATION AT LAKE CITY CALDERA: INSIGHT FROM QUANTITATIVE TEXTURAL AND GEOCHEMICAL ANALYSES By Jordan E. Lubbers A THESIS Submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE In Geology MICHIGAN TECHNOLOGICAL UNIVERSITY 2016 © 2016 Jordan E. Lubbers This thesis has been approved in partial fulfillment of the requirements for the Degree of MASTER OF SCIENCE in Geology. Geological and Mining Engineering and Sciences ThesisDepartment Advisor: ofChad Deering Committee Member: Olivier Bachmann Committee Member: William Rose Department Chair: John Gierke Table of Contents Acknowledgements ................................................................................................................................................. 6 Abstract ....................................................................................................................................................................... 7 1) Introduction ..................................................................................................................................................... 8 1.1 Zoned ignimbrites ....................................................................................................................................... 9 2) Geologic background ................................................................................................................................... 9 2.1 Sunshine Peak Tuff ................................................................................................................................... 10 2.2 Resurgent Intrusive Unit ........................................................................................................................ 10 3) Methods ............................................................................................................................................................ 10 3.1 Petrography ................................................................................................................................................. 10 3.2 iSpectra .......................................................................................................................................................... 11 3.3 Crystal Size Distributions ...................................................................................................................... 11 3.4 Microprobe .................................................................................................................................................. 12 3.5 Cathodoluminescence .............................................................................................................................. 12 3.6 Laser Ablation ............................................................................................................................................ 12 4) Results............................................................................................................................................................... 13 4.1 Petrography ................................................................................................................................................. 13 4.1.1 LSPT, MSPT, rhyolite ...................................................................................................................... 13 4.1.2 USPT trachyte ................................................................................................................................... 13 4.1.3 Syenite .................................................................................................................................................. 14 4.1.4 Mafic Enclaves .................................................................................................................................. 15 4.1.5 Alteration ............................................................................................................................................ 16 4.2 Quantitative textural analysis .............................................................................................................. 17 4.2.1 Crystal size distributions (CSDs) ............................................................................................ 17 4.3 Cathodoluminescence (CL) imaging ................................................................................................. 19 4.4 Mineral chemistry ..................................................................................................................................... 21 4.4.1 Potassium feldspar ........................................................................................................................ 21 4.4.2 Plagioclase ......................................................................................................................................... 23 4.4.3 Quartz ................................................................................................................................................... 24 4.4.4 Biotite.................................................................................................................................................... 26 4.4.5 Fe-Ti oxides ........................................................................................................................................ 29 4.6 Geothermometry ....................................................................................................................................... 29 3 4.6.1 Titanium in quartz geothermometry ................................................................................... 29 5) Discussion ........................................................................................................................................................ 33 5.1 Origin of Sunshine Peak rhyolite........................................................................................................ 33 5.1.1 Thermodynamic modeling ....................................................................................................... 33 5.1.2 Geochemical evidence................................................................................................................. 36 5.1.3 Textural evidence for syenite cumulate formation .................................................... 36 5.1.4 Model for rhyolite production ................................................................................................ 38 5.2 Plutonic-Volcanic connection ............................................................................................................... 39 5.2.1 Textural evidence for trachyte and syenite relationship ....................................... 39 5.2.2 Geochemical signatures as evidence for trachyte and syenite relationship 40 5.3 Evidence for an open-system ................................................................................................................ 41 5.3.1 Disequilibrium textures ............................................................................................................ 41 5.3.1 Crystal size distributions .......................................................................................................... 42 5.3.3 Barium zonation in potassium feldspar ........................................................................... 44 5.3.4 Mechanism for trachyte production ................................................................................... 45 6) Conclusions ..................................................................................................................................................... 46 7) References ....................................................................................................................................................... 47 Appendix 1: Crystal Size Distribution Walkthrough ............................................................................ 53 Equipment Needed ........................................................................................................................................... 53 Programs Used ................................................................................................................................................... 53 Digitizing Image ................................................................................................................................................ 53 To take pictures: ........................................................................................................................................ 53 Creating a mosaic of your thin section .......................................................................................... 54 Outlining grains using Adobe Illustrator ..............................................................................................